1. Field of the Invention
This application is directed to an identification symbol which can be used on items to be identified and, more particularly, to a two-dimensional bar code symbol and a system and method for recognizing and decoding information represented by the symbol.
2. Description of the Related Art
Optical imaging systems are commonly used to decipher data symbols printed on objects in order to identify the objects or to obtain information relating to the object. A bar code symbol is a common one-dimensional form of symbology, and typically comprises a pattern of vertical bars of various widths separated by spaces of various widths. Because the bar and space elements have different light reflecting characteristics, a reader can convert a symbol into an electrical signal by analyzing the light reflected from the symbol. The electrical signal can then be analyzed and decoded to provide an alphanumeric representation of the symbol, which can contain certain information about the object. Bar code symbols of this type are now in common usage in various applications, such as inventory control, point of sale identification, or logistical tracking systems.
Because conventional one-dimensional symbology requires a relatively large amount of space to convey a correspondingly small amount of data, so-called two-dimensional bar code symbologies have been developed. A two-dimensional symbology may comprise a matrix that occupies a uniform amount of space having a generally rectangular or square shape. Instead of bars and spaces, round or square marks disposed at particular rows and columns of the matrix correspond to the information being conveyed. Such two-dimensional symbologies as well as techniques for electronically coding data included therein are well known and are described in, for example, U.S. Pat. No. 5,612,524, U.S. Pat. No. 5,331,176, U.S. Pat. No. 4,972,475, and U.S. Pat. No. 4,924,078, the entire disclosures of which are incorporated herein by reference for all purposes.
Recent applications, however, of two-dimensional symbologies can require encoding of relatively large amounts of information. For example, encoding of biometric information for use on identification cards, bank cards or other types of media can require relatively large amounts of data to be included in a two-dimensional symbol. Thus, there is a need for a two dimensional symbology that can hold such amounts of data.
Additionally, use of such symbologies can include locating a two-dimensional bar code on carrier medium, such as a bank card or ID card, along with other graphic and textual information, such as photographs, textual personal data and/or organization logos. And, the process of reading a two dimensional symbol used in such a context can involve acquiring a photographic image of the entire carrier medium. As such, to read the two dimensional symbol, it needs to be efficiently identified among other graphic information. Additionally, such photographic images can be noisy, distorted, poorly lit and can render an image of the two-dimensional image that may be damaged or otherwise have missing sections. Accordingly, both the two-dimensional symbologies used in such applications and the methods for reading and decoding them need to be able to accommodate noise and distortion, and correct for poor lighting and/or missing sections of a symbol to accurately and efficiently decode such symbols. Further, for use in biometric identification applications such as on a bank card, two-dimensional symbologies should be relatively secure and contain safeguards against fraudulent use or copying.